Sempra herbicide, by Monsanto, now lists pecans on its use label! If yellow and purple nutsedge is a problem in your pecans this herbicide is one you want to consider using.
Sempra contains halosulfuron, a sulfonylurea herbicide, that has proven to provide excellent post emergence control of yellow and purple nutsedge. In addition to nutsedge control, Sempra controls common cocklebur, honeyvine milkweed, Venice mallow, maypop passionflower, pigweed, wild mustard, wild radish, common and giant ragweed, Pennsylvania smartweed, and velvetleaf.
Sempra can be applied as a directed spray in pecan orchards after soil has settled around newly planted trees following rainfall or irrigation. Application rates range from 2/3 to 1-1/3 ounces. The addition of a non-ionic surfactant at 0.5 % v/v (2 qt per 100 gal. of spray solution) is recommended for best results. According to the label extreme care must be taken to avoid contact with tree trunk and leaves. Refer to manufacturers label for use instructions and do not make applications to stressed weeds.